Round Barrow(s)

Folklore

Below the barrow on the south side of the hill is 'Eldon Hole', a scary looking chasm that is known as one of the Wonders of the Peak. It was rumoured to be bottomless. "..in the reign of Elizabeth, the Earl of Leicester is said to have hired a man to go down into Eldon Hole, to observe its form, and ascertain its depth.. 'He was let down about two hundred ells, and, after he had remained at the length of the rope awhile, he was pulled up again, with great expectation of some discoveries; but when he came up he was senseless, and died within eight days of a phrensy.'"
p181 in Museum Europæum; or, Select antiquities ... of nature and art, in Europe; compiled by C. Hulbert (1825)

A two mile plumbline was supposed to have been lowered down without finding the bottom.

This 'Cressbrook' page (with a picture) rather dully says it's only 60m deep. Still quite deep admittedly. Mad people go caving in it.http://www.cressbrook.co.uk/visits/eldonhole.php
People (and sheep) still fall into it and die now and again, so it hasn't lost its scary reputation just yet. Though it may not be the entrance to Hell it was previously thought to be.

A local phrase:

Eldon Hole wants filling up [said as a hint that some statement is untrue].